Circulating aryl hydrocarbon receptor-interacting protein (AIP) is independent of GH secretion.

BACKGROUND: Aryl hydrocarbon receptor-interacting protein (AIP) is evolutionarily conserved and expressed widely throughout the organism. Loss-of-function AIP mutations predispose to young-onset pituitary adenomas. AIP co-localizes with growth hormone in normal and tumorous somatotroph secretory vesicles. AIP protein is detectable in circulation. We aimed to investigate possible AIP and GH co-secretion, by studying serum AIP and GH levels at baseline and after GH stimulation or suppression, in GH deficiency (GHD) and in acromegaly patients. SUBJECTS AND METHODS: Insulin tolerance test (ITT) was performed in GHD patients (n = 13) and age-BMI-matched normal GH axis control patients (n = 31). Oral glucose tolerance test (OGTT) was performed in active acromegaly patients (n = 26) and age-BMI-matched normal GH axis control patients (n = 18). In-house immunometric assay was developed for measuring circulating AIP. RESULTS: Serum AIP levels were in the 0.1 ng/mL range independently of gender, age or BMI. Baseline AIP did not differ between GHD and non-GHD or between acromegaly and patients with no acromegaly. There was no change in peak, trough or area under the curve during OGTT or ITT. Serum AIP did not correlate with GH during ITT or OGTT. CONCLUSIONS: Human circulating serum AIP in vivo was assessed by a novel immunometric assay. AIP levels were independent of age, sex or BMI and unaffected by hypoglycaemia or hyperglycaemia. Despite co-localization in secretory vesicles, AIP and GH did not correlate at baseline or during GH stimulation or suppression tests. A platform of reliable serum AIP measurement is established for further research of its circulatory source, role and impact.

Echocardiography and monitoring patients receiving dopamine agonist therapy for hyperprolactinaemia: a joint position statement of the British Society of Echocardiography, the British Heart Valve Society and the Society for Endocrinology.

This is a joint position statement of the British Society of Echocardiography, the British Heart Valve Society and the Society for Endocrinology on the role of echocardiography in monitoring patients receiving dopamine agonist (DA) therapy for hyperprolactinaemia. (1) Evidence that DA pharmacotherapy causes abnormal valve morphology and dysfunction at doses used in the management of hyperprolactinaemia is extremely limited. Evidence of clinically significant valve pathology is absent, except for isolated case reports around which questions remain. (2) Attributing change in degree of valvular regurgitation, especially in mild and moderate tricuspid regurgitation, to adverse effects of DA in hyperprolactinaemia should be avoided if there are no associated pathological changes in leaflet thickness, restriction or retraction. It must be noted that even where morphological change in leaflet structure and function may be suspected, grading is semi-quantitative on echocardiography and may vary between different machines, ultrasound settings and operators. (3) Decisions regarding discontinuation of medication should only be made after review of serial imaging by an echocardiographer experienced in analysing drug-induced valvulopathy or carcinoid heart disease. (4) A standard transthoracic echocardiogram should be performed before a patient starts DA therapy for hyperprolactinaemia. Repeat transthoracic echocardiography should then be performed at 5 years after starting cabergoline in patients taking a total weekly dose less than or equal to 2 mg. If there has been no change on the 5-year scan, repeat echocardiography could continue at 5-yearly intervals. If a patient is taking more than a total weekly dose of 2 mg, then annual echocardiography is recommended.

Tumor microenvironment defines the invasive phenotype of AIP-mutation-positive pituitary tumors.

The molecular mechanisms leading to aryl hydrocarbon receptor interacting protein (AIP) mutation-induced aggressive, young-onset growth hormone-secreting pituitary tumors are not fully understood. In this study, we have identified that AIP-mutation-positive tumors are infiltrated by a large number of macrophages compared to sporadic tumors. Tissue from pituitary-specific Aip-knockout (AipFlox/Flox;Hesx1Cre/+) mice recapitulated this phenotype. Our human pituitary tumor transcriptome data revealed the "epithelial-to-mesenchymal transition (EMT) pathway" as one of the most significantly altered pathways in AIPpos tumors. Our in vitro data suggest that bone marrow-derived macrophage-conditioned media induces more prominent EMT-like phenotype and enhanced migratory and invasive properties in Aip-knockdown somatomammotroph cells compared to non-targeting controls. We identified that tumor-derived cytokine CCL5 is upregulated in AIP-mutation-positive human adenomas. Aip-knockdown GH3 cell-conditioned media increases macrophage migration, which is inhibited by the CCL5/CCR5 antagonist maraviroc. Our results suggest that a crosstalk between the tumor and its microenvironment plays a key role in the invasive nature of AIP-mutation-positive tumors and the CCL5/CCR5 pathway is a novel potential therapeutic target.

Increased Population Risk of AIP-Related Acromegaly and Gigantism in Ireland.

The aryl hydrocarbon receptor interacting protein (AIP) founder mutation R304* (or p.R304* ; NM_003977.3:c.910C>T, p.Arg304Ter) identified in Northern Ireland (NI) predisposes to acromegaly/gigantism; its population health impact remains unexplored. We measured R304* carrier frequency in 936 Mid Ulster, 1,000 Greater Belfast (both in NI) and 2,094 Republic of Ireland (ROI) volunteers and in 116 NI or ROI acromegaly/gigantism patients. Carrier frequencies were 0.0064 in Mid Ulster (95%CI = 0.0027-0.013; P = 0.0005 vs. ROI), 0.001 in Greater Belfast (0.00011-0.0047) and zero in ROI (0-0.0014). R304* prevalence was elevated in acromegaly/gigantism patients in NI (11/87, 12.6%, P < 0.05), but not in ROI (2/29, 6.8%) versus non-Irish patients (0-2.41%). Haploblock conservation supported a common ancestor for all the 18 identified Irish pedigrees (81 carriers, 30 affected). Time to most recent common ancestor (tMRCA) was 2550 (1,275-5,000) years. tMRCA-based simulations predicted 432 (90-5,175) current carriers, including 86 affected (18-1,035) for 20% penetrance. In conclusion, R304* is frequent in Mid Ulster, resulting in numerous acromegaly/gigantism cases. tMRCA is consistent with historical/folklore accounts of Irish giants. Forward simulations predict many undetected carriers; geographically targeted population screening improves asymptomatic carrier identification, complementing clinical testing of patients/relatives. We generated disease awareness locally, necessary for early diagnosis and improved outcomes of AIP-related disease.

A Follow-Up Study of the Prevalence of Valvular Heart Abnormalities in Hyperprolactinemic Patients Treated With Cabergoline.

CONTEXT: Uncertainty exists whether the long-term use of ergot-derived dopamine agonist (DA) drugs for the treatment of hyperprolactinemia may be associated with clinically significant valvular heart disease and whether current regulatory authority guidelines for echocardiographic screening are clinically appropriate. OBJECTIVE: Our objective was to provide follow-up echocardiographic data on a previously described cohort of patients treated with DA for lactotrope pituitary tumors and to explore possible associations between structural and functional valve abnormalities with the cumulative dose of drug used. DESIGN: Follow-up echocardiographic data were collected from a proportion of our previously reported cohort of patients; all had received continuous DA therapy for at least 2 years in the intervening period. Studies were performed according to British Society of Echocardiography minimum standards for adult transthoracic echocardiography. Generalized estimating equations with backward selection were used to determine odds ratios of valvular heart abnormalities according to tertiles of cumulative cabergoline dose, using the lowest tertile as the reference group. SETTING: Thirteen centers of secondary/tertiary endocrine care across the United Kingdom were included. RESULTS: There were 192 patients (81 males; median age, 51 years; interquartile range [IQR], 42-62). Median (IQR) cumulative cabergoline doses at the first and second echocardiograms were 97 mg (20-377) and 232 mg (91-551), respectively. Median (IQR) duration of uninterrupted cabergoline therapy between echocardiograms was 34 months (24-42). No associations were observed between cumulative doses of dopamine agonist used and the age-corrected prevalence of any valvular abnormality. CONCLUSION: This large UK follow-up study does not support a clinically significant association between the use of DA for the treatment of hyperprolactinemia and cardiac valvulopathy.

Somatic GPR101 Duplication Causing X-Linked Acrogigantism (XLAG)-Diagnosis and Management.

CONTEXT: Recent reports have proposed that sporadic or familial germline Xq26.3 microduplications involving the GPR101 gene are associated with early-onset X-linked acrogigantism (XLAG) with a female preponderance. CASE DESCRIPTION: A 4-year-old boy presented with rapid growth over the previous 2 years. He complained of sporadic headaches and had coarse facial features. His height Z-score was +4.89, and weight Z-score was +5.57. Laboratory testing revealed elevated serum prolactin (185 µg/L; normal, <18 µg/L), IGF-1 (745 µg/L; normal, 64-369 µg/L), and fasting GH > 35.0 µg/L. Magnetic resonance imaging demonstrated a homogenous bulky pituitary gland (18 × 15 × 13 mm) without obvious adenoma. A pituitary biopsy showed hyperplastic pituitary tissue with enlarged cords of GH and prolactin cells. Germline PRKAR1A, MEN1, AIP, DICER1, CDKN1B, and somatic GNAS mutations were negative. Medical management was challenging until institution of continuous sc infusion of short-acting octreotide combined with sc pegvisomant and oral cabergoline. The patient remains well controlled with minimal side effects 7 years after presentation. His phenotype suggested XLAG, but his peripheral leukocyte-, saliva-, and buccal cell-derived DNA tested negative for microduplication in Xq26.3 or GPR101. However, DNA isolated from the pituitary tissue and forearm skin showed duplicated dosage of GPR101, suggesting that he is mosaic for this genetic abnormality. CONCLUSIONS: Our patient is the first to be described with somatic microduplication leading to typical XLAG phenotype. This patient demonstrates that a negative test for Xq26.3 microduplication or GPR101 duplication on peripheral blood DNA does not exclude the diagnosis of XLAG because it can result from a mosaic mutation affecting the pituitary.

Regulation of aryl hydrocarbon receptor interacting protein (AIP) protein expression by MiR-34a in sporadic somatotropinomas.

INTRODUCTION: Patients with germline AIP mutations or low AIP protein expression have large, invasive somatotroph adenomas and poor response to somatostatin analogues (SSA). METHODS: To study the mechanism of low AIP protein expression 31 sporadic somatotropinomas with low (n = 13) or high (n = 18) AIP protein expression were analyzed for expression of AIP messenger RNA (mRNA) and 11 microRNAs (miRNAs) predicted to bind the 3'UTR of AIP. Luciferase reporter assays of wild-type and deletion constructs of AIP-3'UTR were used to study the effect of the selected miRNAs in GH3 cells. Endogenous AIP protein and mRNA levels were measured after miRNA over- and underexpression in HEK293 and GH3 cells. RESULTS: No significant difference was observed in AIP mRNA expression between tumors with low or high AIP protein expression suggesting post-transcriptional regulation. miR-34a was highly expressed in low AIP protein samples compared high AIP protein adenomas and miR-34a levels were inversely correlated with response to SSA therapy. miR-34a inhibited the luciferase-AIP-3'UTR construct, suggesting that miR-34a binds to AIP-3'UTR. Deletion mutants of the 3 different predicted binding sites in AIP-3'UTR identified the c.*6-30 site to be involved in miR-34a's activity. miR-34a overexpression in HEK293 and GH3 cells resulted in inhibition of endogenous AIP protein expression. CONCLUSION: Low AIP protein expression is associated with high miR-34a expression. miR-34a can down-regulate AIP-protein but not RNA expression in vitro. miR-34a is a negative regulator of AIP-protein expression and could be responsible for the low AIP expression observed in somatotropinomas with an invasive phenotype and resistance to SSA.